"The discussion about our system has diverted the focus from the exhaust issue," he said in Australia.

The FIA has clamped down hard on the exhaust-blown diffusers seen throughout the grid last year, but much pre-season chatter focused on some teams' post-ban 2012 solutions that reportedly fly close to the boundaries of the new rules.

But now Germany's Bild newspaper reports that Mercedes suspects Red Bull is also bending the rules in another area.

The report said Mercedes' sound analysis indicated Renault-powered Red Bull is deploying an "illegal engine trick", apparently involving the turning on and off of individual cylinders.

Red Bull RB8. (Photo: Red Bull Racing)

Mercedes' competition vice-president Norbert Haug commented: "There is no official protest by us. But there are some questions that we are asking the FIA."